1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, a semiconductor device and a molding die.
2. Description of the Related Art
A process for manufacturing a semiconductor device is classified broadly into a pre-process for mounting desired elements on a semiconductor wafer and a post-process for packaging semiconductor elements obtained by dividing the semiconductor wafer. The post-process includes a step of sealing the semiconductor elements with a resin.
This sealing step will be described with reference to FIGS. 7A to 7C. In the sealing step, disruption of a balance of resin pressure due to providing a resin on a back surface of an island 206 as shown in FIGS. 7A to 7C may cause various problems. This will be described below.
For example, in a through-gate method shown in FIGS. 5A and 5B, plural cavities are connected in series through runners 44 from a pod 42. This method can shorten distances between the cavities and thus can significantly reduce an amount of molding resin to be consumed. Therefore, the through-gate method is an excellent method which can also increase the number of elements per unit area of die and improve manufacturing efficiency. This method has been reported by Junichi Saeki et al. in Japanese Patent Application Publication No. Hei 1-205432, for example.
FIGS. 7A to 7C show two cavities in the method described above. With reference to FIG. 7A, plural cavities 200A and 200B are provided in a molding die and the cavities 200A and 200B communicate with each other through a runner 202. In each of the cavities 200A and 200B, an island 206 having a semiconductor element 204 mounted on its upper surface is housed.
With reference to FIG. 7B, next, a sealing resin is injected into each of the cavities 200A and 200B. Specifically, an unillustrated pod is connected on the left side of the cavity 200A, and a liquid resin supplied from the pod is first injected into the cavity 200A and then supplied to the cavity 200B through the runner 202. In FIG. 7B, a flow of the sealing resin is indicated by bold arrows. A part of a sealing resin 210 injected into the cavity 200A is injected below the island 206 and the rest thereof is injected above the island 206. Note that pressing pins P are provided for the island 206, because the island 206 is inevitably pushed up by the resin thinly applied on the back surface of the island 206. These pressing pins are provided in portions indicated by circled x shown in FIG. 5A in a TO220 package, for example.
Furthermore, the above resin sealing method using the molding die is described for instance in Japanese Patent Application Publication No. 2004-158539.
However, the above sealing resin injection method has a problem that the island 206 is moved by an injection pressure of the resin injected into the cavity 200A.
Specifically, when viewed in a cross-sectional view of FIG. 7B, the resin entering the cavity 200A from a gate G2 is roughly divided into a resin entering a space between the back surface of the island 206 and the lower die and a resin injected into a space between a front surface of the island 206 and the upper die. Since the space between the back surface of the island 206 and the lower die has a smaller volume, the space is first fully filled with the resin and the resin applies an upward force to the island 206. However, the pins P suppress a rise of the island 206.
On the other hand, since the space between the front surface of the island 206 and the upper die has a larger volume, the resin is subsequently fully filled. However, the gates G2 and G1 are arranged on the same level in height as or below the arrangement position of the island 206 in order to fill the resin below the back surface of the island. The filled resin flows downward toward the outlet G1 and thus a downward force acts on the right end of the island 206 as indicated by a downward arrow AL1. Specifically, in FIG. 7B, the right side of the island 206 is lowered with a contact point of the left pin P as a fulcrum point.
Accordingly, the thickness of the sealing resin covering the back surface of the island 206 is reduced. Thus, there is a possibility that a predetermined breakdown voltage cannot be obtained. This also leads to deterioration in moisture resistance.
Moreover, FIG. 7C shows a general IC package. In this package, a resin is also filled below a back surface of an island 206A. In this case, the resin moves in the same manner as shown in FIG. 7B, and a thin metal wire FW near a gate G1 is pressed downward and deformed by a resin pressure or even comes into contact with a corner of the chip in a worse case. Moreover, an inner lead may be deformed.
The present invention is capable of providing a highly reliable product by adjusting attachment positions of runners in the through-gate method.